1. Field of the Invention
The present invention generally relates to integrated circuit fabrication process, and more particularly relates to a barrier layer removal method and a semiconductor structure forming method.
2. The Related Art
In a semiconductor structure, a traditional material for forming electronic circuitry is aluminum. But as the feature size of integrated circuit has decreased, aluminum is no longer fit for forming the electronic circuitry in the semiconductor structure because aluminum has high resistance. Copper which has a good electrical conductivity replaces aluminum and is used in the integrated circuit. But copper has a defect that copper is easy to diffuse to SiO2, which seriously affects the performance of the integrated circuit. Therefore, to solve the issue, a barrier layer is used for preventing the copper from diffusing to the SiO2.
At present, the material of the barrier layer normally chooses tantalum (Ta), tantalum nitride (TaN), titanium (Ti) or titanium nitride (TiN) and the barrier layer formed on non-recessed areas of the semiconductor structure is removed mainly by chemical mechanical polishing (CMP). For 20 nm or below 20 nm node process, the thickness of the barrier layer must be enough thin. For the barrier layer of tantalum, tantalum nitride, titanium or titanium nitride, if the thickness of the barrier layer of tantalum, tantalum nitride, titanium or titanium nitride is too thin, the ability of the barrier layer for preventing copper from diffusing to SiO2 will reduce, so the barrier layer of tantalum, tantalum nitride, titanium or titanium nitride is not fit for 20 nm or below 20 nm node process.
Hence, there needs to find new material to form the barrier layer in 20 nm or below 20 nm node process. Facts proved that cobalt (Co) or ruthenium (Ru) can be used for forming the barrier layer. The ability of cobalt or ruthenium for preventing copper from diffusing to SiO2 is much stronger than that of tantalum, tantalum nitride, titanium or titanium nitride. But when using the cobalt as the barrier layer in a semiconductor structure, potential chemical corrosion of cobalt liner along sidewall of recessed area (such as trench, via) happens during chemical mechanical polishing the barrier layer when the liner is in contract with slurry. Galvanic corrosion issues on top of the recessed area exist where the copper forms a galvanic couple with the cobalt liner. Relatively, the hardness of ruthenium is high. When chemical mechanical polishing the barrier layer of ruthenium, it is easy to generate scratches.
Therefore, due to the properties of the new material, the barrier layer is hard to remove by CMP, which induces a bottleneck of the new material industrialization.